I'd suggest checking the assays printed on the bottle for possible contaminants.  Solvent brands have made a difference in processes that I have run in the past.  How sensitive are you to water?  After 10 years it might not be as dry as a fresh bottle.  To seek out its decomposition with time, try searching in SciFinder Scholar or ISI.

Water shouldn't make the diethylenetriamine precipitate.   That's true for any trace contaminants. 

I guess it is a matter of curiosity, not really a practical issue. Moisture and acetonitrile hydrolysis products are the first things that come to mind. Could it be a trace of acetamide or acetic acid (or rather ammonium acetate) ? Another possibility is the presence of oxidation products - typical for diethyl ether and THF, but not as much for acetonitrile, although after 10 years, who knows ...

I also think that diethylenetriamine can potentially form carbonate if exposed to air (which now contains about 400 ppm of CO2 !).

Thanks!   Well,  I cracked open a new bottle and didn't see any precipitation.   That's the second time I got burned with bad solvent in my lab.   Once with degraded dichloromethane that destroyed plastic parts in my HPLC, probably because of HCL formation,  and now this.   That's what happens when working in the same lab with several people.   I must start getting everything fresh for my work.